The generation of microwave-frequency signals of millimetric wave type (RF radio wave of frequency between 30 GHz and 300 GHz) and of TeraHertz type (frequency between 100 GHz and 10 THz) exhibits numerous applications in the fields of detection, spectroscopy and high-bitrate wireless data transmission. In the latter field, the higher the support frequency, the more significant the bitrate that can be transported. By way of example, for a 1-GHz carrier, a maximum bitrate of 1 Gbit/s is obtained, whilst with a carrier of 1 THz, bitrates of 10 to 20 Gbit/s are possible, hence the interest in developing components capable of emitting in this range of frequencies with sufficient power.
A first solution according to the prior art is a component 100 able to emit a signal S of microwave frequency F, illustrated in FIGS. 1a-1b (FIG. 1a perspective view and FIG. 1b view from above). This unitary photodiode 100 comprises a planar guide 10 in which two optical waves propagate, a wave O1 of wavelength λ1 and a wave O2 of wavelength λ2, and an associated photo-mixer 11 of small size. λ1 and λ2 are such that they exhibit a heterodyne beat, that is to say that the modulus of the difference f1−f2 of the associated optical frequencies f1 and f2 is equal to a frequency F in the microwave-frequency domain:f1=C/λ1f2=C/λ2F=|f1−f2| of the order of a TeraHz.
The optical waves are coupled to the photo-mixer 11 by evanescent coupling in such a way that the latter generates a wave at the frequency F.
The photodiode 100 also comprises a metal antenna 12, exhibiting a bowknot shape, coupled to the photo-mixer 11, and which radiates an electromagnetic signal S of frequency F into space.
The photo-mixer length l10 is typically from 10 to 20 μm since it is necessary to limit the parasitic capacitance that the device would exhibit and which would strongly attenuate the signal detected at the frequency F. Moreover, a lengthening would not make it possible to increase the absorbed power, the major part of the light being absorbed in the first 10 microns of the component.
The width L10 is dimensioned to be of the order of magnitude of the optical wavelengths, typically 2 to 3 times greater, but not more.
Indeed, L10 must remain small enough for the component to operate correctly beyond 30 GHz. When L10 becomes too large, the transport of the signal at the semi-conductor (photo-mixer 11)/metal (antenna 12) interface is degraded by the presence of parasitic capacitances (capacitive effects and transit time effects) the effect of which is to attenuate the photogenerated signal S of frequency F.
The dimensional limitation of L10 has the drawback of limiting the power that can be radiated.
Moreover, the small dimension of the component 100 compels the use of an antenna 12 in order to accommodate the size of the RF mode of the signal S.
A second solution according to the prior art is a system 200 able to emit a signal S of microwave frequency F, based on an integration of planar photodiodes arranged as a 2D matrix or of an emitter of large surface area in the form of a large-size photodiode, such as illustrated in FIG. 2. The optical waves O1 and O2 are directly incident on a side of the component PM which radiates the signal of frequency F on the opposite side.
This solution exhibits low effectiveness of coupling because the photo-mixer PM consists of a layer of small thickness, thus limiting the interaction between the light and the photo-mixer. Moreover, to polarize each photo-mixer of the matrix, it is necessary to produce opaque electrodes which reduce the area of interaction between the light and the photo-mixers.
Its implementation with discrete optical elements for shaping the signals O1 and O2 renders the system 200 bulky. Moreover, this system does not make it possible to integrate on the same wafer other functions which interact with light such as amplification, modulation of amplitude or of phase. Furthermore, 2D matrices do not make it possible to localize the illumination in the zones where photo-detection is desired in an effective manner, thereby limiting the high-frequency power generated/incident optical power efficiency.
When it is sought to introduce a scan of a radio wave in the millimetric range, current solutions exhibit several drawbacks. A solution based on discrete optical components is bulky and the signal emitted exhibits strong divergence. An alternative solution based on mechanical elements is also bulky, and comprises a mobile element which is not compatible with all systems.
An aim of the present invention is to alleviate the aforementioned drawbacks and more particularly to produce an integrated optoelectronic component able to generate and radiate a microwave-frequency signal (also referred to as a high-frequency signal) without any antenna.